Receiving system



\Feb. 17, 1942.

A. VAN WEEL 2,273,546

RECEIVING SYSTEM Filed June 25, 1940 I TELEVISION AUXILIARY CATHODE ANOOE INVENTOR. ADELBERT AN WEEL BY 7 M ATTORNEY Patented Feb. 17, 1942 RECEIVING SYSTEM Adelbert van Weel, Eindhoven, Netherlands, assignor to Radio Corporation of America, a corporation oi Delaware Application June 25, 1940, Serial No. 342,263 In'the Netherlands October 10, 1939 2 Claims. (Cl. 178-53) In the application of Johan Haanties et al., Ser. No. 334,502,1iled May 11, 1940, there is described a circuit arrangement for amplifying and for separating, if desired after mixing with a .lo-

cal oscillation, two or more oscillations.

In this circuit arrangement use is made of a tube having, among other things, a control grid, at least one secondary-emitting auxiliary cath ode and an anode. The oscillations to be amplifled and to be separated are supplied to the control grid of the said tube, if desired jointly with a local oscillation. In the circuit of the auxiliary cathode and in the anode circuit of the tube there are included 'impedances having respectively a high value for each of the oscillations to be separated or for each of the intermediate-frequency oscillations corresponding to each of the oscillations to be separated.

If in such a circuit arrangement only two oscillations are to be separated, use may advantageously be made of a discharge tube having, among other things, an auxiliary cathode, a plate-shaped anode arranged outside the paths of the electrons passing from the cathode to the auxiliary cathode, and a grid-shaped electrode arranged at a short distance in front of the auxiliary cathode and approximately parallel thereto and connected in a conductive manner to the anode. An example of such tube is described and claimed in the copending application of Van Overbeek, Ser. No. 190,531, filed February 15, 1938. In this tube the grid-shaped electrode serves to facilitate the emerging of secondary electrons from the auxiliary cathode.

In the circuit arrangement in question the fact of the grid-shaped electrode being connected in a conductive manner to the anode entails, however, a disadvantage. In fact, the capacity between the auxiliary cathode and the anode constituted by the plate-shaped anode and the gridshaped electrode causes a coupling between the circuits in which the oscillations to be separated occur, resulting in the establishment of a good separation being possible only .with difficulty.

The invention is based on recognition of the fact that this capacity is mainly determined by the capacity between the grid-shaped electrode and the auxiliary cathode. In fact, the gridshaped electrode is at a short-distance in front of and parallel to the auxiliary cathode, whilst the plate-shaped anode'is arranged at some distance from and not parallel to the auxiliary cathode.

According to the invention, when using a tube having a plate-shaped anode located outside the paths of the electrons passing from the cathode to the auxiliary cathode and in which a gridshaped' electrode is arranged at a short distance in front of the auxiliary cathode and approximately in parallel thereto, this grid-shaped electrode which has a high positive potential is connected to the cathode through an impedancewhich is negligible for alternating current.

The invention will be more clearly understood by reference to the accompanying drawing showing, by way of example, one embodiment thereof.

Fig. 1 shows a circuit arrangement according to the invention.

Fig. 2 shows a section of a tube to be used in the circuit arrangement of Fig. 1.

In Fig. l, l denotes a tube containing a cathode 2, a control grid 3, a screen grid 4, a secondary emitting auxiliary cathode 5, an anode 6 and a grid-shaped electrode IS. 'The cathode 2 is connected to earth through the parallel connection of a resistance 1 and a condenser 8 which serves for automatic negative grid voltage. The oscillations to be amplified and to be separated which originate from a high-frequency amplifier which is not shown in the drawing are supplied to the control grid 3 by an oscillatory circuit 9.

These oscillations control the electronic current emitted by the cathode 2 which current is accelerated by the screen grid 4, passes to the auxiliary cathode 5 and at this point causes the emission, by means of electron bombardment, of a number of secondary electrons proportional to the said current, which electrons accelerated by a grid-shaped electrode l5 pass to the anode 6. The grid-shaped electrode I5 is connected to the cathode 2 through a condenser 16 having an impedance which is negligible for the oscillations to be separated. This results in an electronic current comprising the oscillations supplied to the control grid 3 flowing both in the circuit ill of the auxiliary cathode and in the anode circuit H.

In the circuit Ill of the auxiliary cathode there is included an oscillatory circuit I2 which is tuned to one of the oscillations to be separated, for example the sound modulated carried frequency, and coupled to an oscillatory circuit l3, to which this oscillation is transmitted.

The anode circuit ii of the tube l comprises an oscillatory circuit I 8 tuned to another oscillation, for example the television modulated carrier frequency, and coupled to an oscillatory circuit IQ to which this oscillation is transmitted. The oscillations to be separated are respectively derived from the oscillatory circuits l3 and I9.

In the electrode system represented in Fig. 2, 3| denotes a cathode surrounded by a control grid 32 and a screen grid 33. The electrons emitted by the cathode 3| flow along paths 34 to a secondary-emitting auxiliary cathode 35 where secondary electrons are dislodged. These secondary electrons are sucked away by a gridshaped lectrode 36 and pass to an anode 31. A screen electrode 38 serves to form an electrostatic fleld which determines the electron paths 34.

The tube furtherv contains a screen 39 which is arranged at such a point that material which may vaporise from the primary cathode 3| cannot reach the auxiliary cathode 35.

Th grid-shaped electrode 36 is led out separately and is set up outside the tube at a high positive potential and connected to the cathode through an impedance negligible for alternating current.

The grid-shaped electrode may alternatively be connected inside the envelope of the discharge tube across a resistance or a choke to the anode and across a condenser to the cathode. In this case the grid-shaped electrode need not be led out separately.

What I claim is:

1. A circuit for amplifying and separating two signal-modulated carriers of difierent frequencies, comprising an electron discharge tube having at least a cathode, a control grid, a secondary-emitting auxiliary cathode and an anode, means for simultaneously impressing both carrier frequencies upon the control grid, a pair of impedances each included respectively in the circuit of the auxiliary cathode and in that of the anode and each having respectively a high value for one of the carrier frequencies to be separated, the anode of said tube being disposed outside the path of the electrons passing from the cathode to the auxiliary cathode, a grid-shaped electrode electrically separated from said anode within the tube arranged at a short distance in front of the auxiliary cathode and approximately parallel to the latter, said grid-shaped electrode having impressed thereon a high positive potential and being connected to the cathode through an impedance which is negligible for alternating current.

2. In a combined sound and television receiver, a circuit for amplifying and separating the sound and television signal frequencies, comprising an electron discharge tube having at least a cathode for emitting primary electrons, a signal input electrode, an auxiliary cathode adapted to emit secondary electronsdisposed in a path to receive electrons from the primary cathode, and an anode disposed outside the path of the primary electrons, an input circuit simultaneously responsive to both the sound and television signal frequencies connected between the input electrode and primary cathode, an output circuit connected to the anode including an impedance of high value to one of the signal frequencies, a second output circuit connected to the auxiliary cathode including an impedance of high value to the other of said signal frequencies, a grid-shaped electrode disposed adjacent the auxiliary cathode and electrically separated from the anode within the tube having impressed thereon a high positive potential, and a signal frequency by-pass condenser connected between the gridshaped electrode and the primary cathode.

ADELBERT VAN WEEL. 

